As a safety device to avoid serious railway accidents, such as train collisions due to the failure of a train crew on a running railway train to recognize a signal, there has heretofore been known an automatic train stopping control system (ATS), whereby an alarm is issued to a train about to enter a danger zone, and when the speed of a train which has entered the danger zone exceeds a distance-speed pattern for the specific train, braking is automatically carried out to bring the train to a halt at a specific spot.
As described later with reference to FIGS. 1(a) and 1(b), such an automatic train stop control device consists of ground units and a train unit. The ground units are distributed along the track and successively react to the aspects of a signal which changes with the progress of the train, sending the signal aspects to the train unit carried by the train. The train unit in response to the information transmitted from the ground units generates a distance-speed train pattern specific to the train and causes the brakes of the train to be applied if the train speed exceeds the speed of the distance-speed train pattern.
Depending on the mode of control, the conventional automatic train stopping systems may be roughly classified into two types: a spot control type in which control information is transmitted in response to signal aspects of a block section signal to a train at specific spots only, and a continuous control type in which the control information is continuously transmitted to a train through a track circuit or the like. The two types possess various advantageous features and it is difficult to decide which is better. However, the spot control type, which has a relatively simple system configuration including the ground equipment, is superior to the continuous control type in terms of ease of equipment maintainance and cost.
Among various types of systems into which the spot control type of systems may be subdivided, the most desirable is the train pattern type system which permits setting a distance speed train braking pattern in accordance with the braking performance of the train.
The train pattern type systems can be still further divided into a two-stage pattern type system in which a distance-speed braking pattern specific to the train and which corresponds to the stop aspect (R) and caution aspect (Y) of a block section signal can be generated on the train at a specific pattern-generating spot ahead of, with respect to the direction of movement of the train, the signal, and which is determined by the longest braking distance for the train, and a single-stage pattern type system in which only a pattern corresponding to the stop aspect (R) of the block section signal can be generated on the train.
On a railway line where the signal block section is long enough and the pattern-generating spots are located within a block section next preceding the relevant block section signal, there is fundamentally no difference between the single-stage pattern type system and the two-stage pattern type system, because in either case there is no possibility of the patterns overlapping in the same block section. But on a line where short block sections succeed one another and the pattern-generating spots occur ahead of a block section signal located ahead of the relevant block section signal there is a possibility of the pattern overlapping. From the standpoint of the logic of generating train control systems, a single-stage pattern type system would be preferable if said pattern were to be applied as a common ATS to diverse trains with different braking performances. Even with a single-stage pattern type system, insofar as the pattern overlap is concerned, where the quantity of information required will amount to the number of signals times the number of information spots and numerous patterns will need to be memorized, executed patterns cancelled, and patterns selected for execution, the pattern-generation logic becomes complicated and in consequence the advantages of the spot control, i.e. simplicity and economy, will be lost.